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Nitrous Oxide and Methane Fluxes from Urine and Dung Deposited on Kenyan Pastures
Author(s) -
Tully Katherine L.,
Abwanda Sheila,
Thiong'o Margaret,
Mutuo Paul M.,
Rosenstock Todd S.
Publication year - 2017
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2017.01.0040
Subject(s) - dry season , nitrous oxide , urine , zoology , wet season , kenya , livestock , grazing , greenhouse gas , environmental science , chemistry , agronomy , environmental chemistry , biology , ecology , biochemistry , organic chemistry
Livestock keeping is ubiquitous in tropical Africa. Urine and dung from livestock release greenhouse gases (GHGs), such as nitrous oxide (N 2 O) and methane (CH 4 ), to the atmosphere. However, the extent of GHG's impact is uncertain due to the lack of in situ measurements in the region. Here we measured N 2 O and CH 4 emissions from cow urine and dung depositions in two Kenyan pastures that received different amounts of rainfall using static chambers across wet and dry seasons. Cumulative N 2 O emissions were greater under dung+urine and urine‐only patches ( P < 0.0001), more than three times higher in the wet compared with the dry season ( P < 0.0001), and higher in the farm receiving higher rainfall overall ( P < 0.0001). Cumulative CH 4 emissions differed across treatments ( P = 0.012), driven primarily by soil CH 4 uptake from the urine‐only treatment. Cumulative N 2 O emissions were positively related to N input rate in excreta. However, the relationship was linear during the dry season ( r 2 = 0.99; P = 0.001) and exponential during the wet season ( r 2 = 0.99; P < 0.0001). Nitrous oxide emission factors were 0.05% (dry season) and 0.18% (wet season) of N in urine and dung+urine, which is less than 10% of the IPCC Default Tier 1 emission factor of 2%. We predict that emissions from cattle urine in Kenya are approximately 1.7 Gg N 2 O–N yr −1 (FAO estimates 11.9 Gg N 2 O–N yr −1 ). Our findings suggest that current estimates may overestimate the contribution of excreta to national GHG emissions and that emission factors from urine and dung need to account for agroecosystems with distinct wet and dry seasons. Core Ideas Urine and dung deposited on pasture are a significant agricultural source of GHGs. N 2 O emissions from African cattle excreta were higher in the wet than dry season. Urine and the combination of urine and dung had the highest N 2 O fluxes across seasons. N 2 O emissions were positively correlated with excreta N. N 2 O emission factors from excreta were one‐tenth that predicted by the IPCC.